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Deux nouveaux modèles de ligne l'écoulement ont été proposés; un nouveau « fan-modèle » (FM) et un « modèle de loi-puissance » généralisé (PLM). Le FM est examiné sur les lignes d'écoulement expérimentalement obtenues pour Al par une ECAE de 90° et de 120°. Le PLM est comparé également aux champs d'écoulement obtenus à partir des simulations d'éléments finis. Pour le PLM, les effets de ses paramètres sur le taux maximum de déformation et la déformation équivalente de von Mises sont analysés. Les lignes d'écoulement expérimentales de l'Al dans les ECAE à 90° et 120° sont analysées avec le PLM. En utilisant le PLM, l'effet de la contre-pression sur le champ de déformation dans une ECAE ECAE de 90° pour un alliage d'aluminium 6061 est analysé. L'application de ces deux modèles dans la simulation de texture est présentée. L'effet de chaque paramètre de PLM sur le développement de texture dans la ECAE de 90° et de 135° a été simulé. La comparaison des textures simulées avec celles de l'expérience pour le Cu et l'Al obtenus à partir des essais ECAE à 135° est présentée et les différences entre elles ont été discutées. Les simulations de texture pour le Cu extrudé par une ECAE à 90° employant le modèle ligne d'écoulement appelé fan-type sont faites. L'extrusion angulaire de canal non-égal (NECAE) comme nouveau procédé de SPD est également présentée. Le changement de forme d'un élément de matière pendant ce procédé dans une matrice à 90° est étudié et une nouvelle fonction de ligne d'écoulement est proposée. En outre, le développement de texture dans NECAE est simulé et comparé aux textures dans le procédé d'ECAE / Two new flow line models were proposed; a new “fan-model” (FM) and a generalized “power-law model” (PLM). The FM is tested on experimentally obtained flow lines in Al ECAE processed through a 90° and a120° die. The PLM is compared also with the flow fields obtained from finite element simulations. For the PLM, the effects of its parameters on the maximum strain rate and von Mises equivalent strain are analysed. The experimental flow lines in ECAE deformed Al are analyzed with regard to these parameters and their variation within the 90° and 120° dies is discussed. Using the PLM, the effect of the back pressure on the deformation field in a 90° ECAE die for an aluminium alloy 6061 is analysed. Application of these two models in texture simulation is presented. The effects of each parameter of PLM on texture development in 90° and 135° ECAE die have been simulated. The comparison of simulated textures with those from experiment for Cu and Al obtained from 135° ECAE tests was presented and the differences between them were discussed. The texture simulations for Cu ECAE processed through a 90° die using the fan-type flow line model is done with a very good agreement with experiment. The non-equal channel angular extrusion (NECAE) as a new SPD process is also presented. Material element shape change during this process within a 90° die is studied and a new flow line function is presented and validated using finite element simulations. Furthermore, texture development in NECAE is simulated and compared with the textures of the ECAE process

This research investigated the effectiveness of equal channel angular extrusion (ECAE) and annealing to improve the grain morphology and mechanical properties of electron-beam remelted pure niobium. Extrusions were performed at room temperature with a 90o die. Routes 1A, 2C, 4E and 8E were investigated with duplicate billets undergoing routes 1A, 2C and 4E to determine reproducibility. Niobium proved to be very workable during the ECAE process. Hardness increased most dramatically after the first pass and leveled off thereafter. Recrystallization temperatures for the Reference Metals material ranged from a low of 800o C for routes 2C, 4E and 8E to a high of 1000o C for route 1A. For the Wah Chang material, the recrystallization temperatures ranged from a low of 800o C for the 4E ECAE processed material to a high of 950o C for the asreceived material. The initial grain size and orientation have been hypothesized to be influential on recrystallized grain morphology for ECAE/annealing processed niobium. Smaller initial grains produce a smaller and more homogeneous recrystallized grain microstructure. The average grain diameters for the recrystallized 4E ECAE processed Wah Chang material are 13 ± 6.3 mm for the 1000o C annealed state (no banding) and are 21 ± 9.5 mm for the 1100o C annealed state (no banding). Reference Metals material that underwent route 4E and annealed at 1000o C resulted in an average grain diameter of 28 mm for billet 2 (banding) and an average grain diameter of 32 mm for billet 19 (slight banding). Reference Metals material that underwent route 8E (no banding) annealed at 1000o C resulted in an average grain diameter of 36 mm. Reference Metals material that underwent route 4E samples annealed at 1100o C resulted in an average grain diameter of 26 mm for billet 2 (banding) and an average grain diameter of 43 mm for billet 19 (slight banding). Route 8E (significant banding) annealed at 1100o C resulted in an average grain diameter of 29 mm. Strain failure decreases from the as-cast material to the worked/recrystallized material while the 0.2% yield stress and ultimate tensile strength increase from the as-cast material to the worked/recrystallized material. Long sub-grains are created in the as-worked material after one and two passes and become more broken up after four passes. Sub-grain boundary angles increase with increasing strain. To produce a fine and homogeneous microstructure from large grained niobium, intermediate annealing should be employed.

Ultrafine grained (UFG) and nanocrystalline materials have attracted considerable interest because of their unique mechanical properties as compared with coarse grained conventional materials. The fabrication of relatively large amounts of these materials still remains a challenge, and a thorough understanding of the relationship between microstructure and mechanical properties is lacking. The objective of this study was to investigate the mechanical properties of UFG and nanocrystalline copper obtained respectively by a top down approach of severe plastic deformation of wrought copper and a bottom up approach of consolidation of copper nanoparticles using equal channel angular extrusion (ECAE). A critical assessment and correlation of the mechanical behavior of ECAE processed materials to the microstructure was established through the determination of the effect of strain level and strain path on the evolution of strength, ductility and yield anisotropy in UFG oxygen free high conductivity copper in correlation with grain size, grain morphology and texture. ECAE was shown to be a viable method to fabricate relatively large nanocrystalline consolidates with excellent mechanical properties. Tensile strengths as high as 790 MPa and fracture strain of 7 % were achieved for consolidated 130nm copper powder. The effects of extrusion route, number of passes and extrusion rate on consolidation performance were evaluated. The relatively large strain observed was attributed to the bimodal grain size distribution and accommodation by large grains. The formation of bimodal grain size distribution also explains the simultaneous increase in strength and ductility of ECAE processed wrought Cu with number of passes. Texture alone cannot explain the mechanical anisotropy in UFG wrought copper but we showed that grain morphology has a strong impact and competes with texture and grain refinement in controlling the resulting yield strength. Tension-compression asymmetry was observed in UFG wrought copper. This asymmetry is not always in favor of compression as reported in literature, and is also influenced by grain morphology through the interaction of dislocations with grain boundaries. Different prestrains in tension and compression should be experimented to have a better understanding of the encountered anisotropy in Bauschinger parameter in relation with the observed tension-compression asymmetry.

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Equal Channel Angular Extrusion (ECAE) has great potential for developing ultrafine grain structure consisting of homogeneous and equiaxed grains dominated by high angle grain boundaries. In addition, the ECAE-processed specimens retain their original cross-section, providing capabilities of multi-passing. However, the process is discontinuous as the length of the billet is limited due to potential buckling of the extruding ram. This problem provides an opportunity of making the process continuous. The objectives of this study were to examine the feasibility of a process obtained by combining ECAE and Equal Channel Angular Drawing (ECAD), evaluate the potential of the combined process for continuous processing of sheet metal, and to analyze the mechanical response of sheet metal subjected to the ECAE and ECAD techniques using numerical study. Numerical analyses of ECAE and ECAD were performed using the commercial FE analysis package ABAQUS/explicit. Experimental data and analytical models available in literature were used to validate the numerical results. Parametric studies on the effects of drawing angle, and sheet thickness to die radius ratio (t/r), on reduction in thickness, strain uniformity and resulting microstructure are presented. Numerical results indicate that ECAD through a closed channel should be preferred over conventional drawing (open channel) operation as reduction in thickness is decreased by 2-3% after a single pass. In the experimental study, it was observed that during ECAD, the reduction in thickness increases by 2.5-3.5% per pass. Also, a higher reduction is observed in route C compared to route A. Use of sharper die corners (higher t/r ratios) and smaller channel intersection angles tend to increase this thickness reduction, and results in an increase in hardness i.e., results in strengthening. ECAD most likely results in a non-uniform microstructure with low fraction of high angle grain boundaries. In addition, for a given pass, the average hardness of the ECADprocessed samples is approximately half that of ECAE-processed samples. This suggests that ECAD alone may not be commercially viable. However, a significant improvement in minimizing reduction in thickness is achieved by providing a little gap between the sheet metal and support plates. From the numerical analyses, the proposed continuous process appears to be effective in retaining continuity of the drawing operation, minimizing the percent reduction in thickness and imparting higher plastic strains. It is believed that an experimental study of the process will reveal some more promising information.

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Magnesium and its alloys have been considered as alternatives to aluminum alloys and steels for structural applications in automotive and aerospace applications due to their superior specific strength and light-weight. However, they have hexagonal-close packed (hcp) structure, and thus have a small number of deformation systems resulting in low ductility and formability near room temperature, anisotropic thermo-mechanical response and strong deformation textures. The aim of this work is to investigate experimentally the effect of crystallographic texture generated during severe plastic deformation (SPD), on the subsequent formability and mechanical flow anisotropy in AZ31B Mg alloy. The proper control of grain size and texture through SPD is expected to result in better low temperature formability and better control of mechanical flow anisotropy. AZ31B Mg alloy has been successfully processed using equal channel angular extrusion (ECAE) following different processing routes, multiple passes, and different processing temperatures, in order to obtain samples with a wide variety of grain sizes, ranging from ~370 nm up to few microns, and crystallographic textures. Low temperature processing of the AZ31B Mg alloy was successful after initial high temperature processing. Smaller grain sizes were achieved using the temperature step-down method leading to incremental reduction in grain size at each ECAE pass. The temperature step-down method was utilized to develop hybrid ECAE routes to obtain specific crystallographic textures. Optimized hybrid ECAE routes were developed which resulted in a high strength/high ductility material with the average grain size of ~370 nm. The ECAE processed alloy showed a high tensile yield strength of ~380 MPa that has never been reported so far in AZ31 ingot metallurgy Mg alloys. The influence of grain size on the critical stress for the activation of individual deformation mechanisms was also investigated by systematically controlling the texture and grain size, and assuming the activation of mainly a single deformation mechanism through the careful selection of the loading direction on the processed samples. It was revealed that the Hall-Petch slope for the basal slip was much smaller than those of prismatic slip and tensile twinning.

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